s Speciation and Infrageneric Classification in the Planktonic Dinoflagellate Tripos (Gonyaulacales, Dinophyceae)

Background: The genus Tripos, formerly known as marine species of Ceratium, is the dinoflagellate with the greatest number of species and infraspecific taxa (~800) due to the high morphological intraspecific variability of numerous species. In the past, the species of Tripos were proposed into distinct genera. Objective: To propose an infrageneric classification and to review the taxonomy and nomenclature of each taxon in order to establish the correct species and synonymy. Methods: Observations from the Mediterranean Sea, and Atlantic and Pacific Oceans, a review of the original descriptions and further literature, and the available molecular data. Results: A re-instatement of this generic split is not justified due to the difficulties to circumscribe the basal subgenera Amphiceratium and Archaeceratium, and the polyphyletic character of Biceratium. The subgenus Amphiceratium is dismembered after the classification of the sections Inflata and partially Fusiformia into Archaeceratium. The subgenus Tripos (autonym) replaces other names such as Tripoceratium or Orthoceratium. Based on the original descriptions, the records of T. furca and T. lineatus correspond to T. eugrammus and T. furca, respectively, and T. macroceros has been reported as T. contrarius. The names T. belone and T. carriensis have been misapplied for T. pacificus and T. volans, respectively. Tripos arcuatus, T. gracilis, T. inclinatus, T. scapiformis and T. subcontortus are revived to replace T. euarcuatus, T. declinatus, T. horridus, T. longirostrum and T. contortus, respectively. The species T. ramakrishnae and T. fusus var. schuettii were described from individuals infected by endoparasites. Tripos rotundatus comb. nov. is proposed for C. digitatum var. rotundatum. Conclusion: Tripos is restricted to 57 correct species, although the speciation and synonymy are incomplete due to lack of studies in the life cycle and molecular data.